1. Field of the Invention
This invention relates generally to method for reducing line edge roughness of patterned photoresist, and particularly relates to a method for improving precision of pattern of patterned photoresist without changing patterned photoresist material or changing both is develop process and bake process.
2. Description of the Prior Art
For semiconductor fabrication, patterned photoresist is an indispensable part for transferring pattern of a mask into a semiconductor substrate. Because the pattern of patterned photoresist essential is the pattern of the semiconductor substrate, how to ensure the pattern of patterned photoresist is equal to the mask is an important key for whether the pattern is accurately transferred or not.
Because practical semiconductor fabrication is limited by numerous factors, such as available materials of both patterned photoresist and a developer, unavoidable errors during both developing process and priming process, standing wave phenomena, and non-uniform distribution of polymers which are composition of patterned photoresist. It is usually that some trenches are existent in formed patterned photoresist that is patterned. Owing to location and number of trenches are random distributed, disadvantages such as non-smooth surface and line width variation is occurred and usually is called as line edge roughness. FIG. 1A and FIG. 1B illustrate ideal shape of patterned photoresist, and both FIG. 1C and FIG. 1D qualitatively show real shape of patterned photoresist while line edge roughness is happened. Herein, all figures are not illustrated in according to practical scale for emphasizing possible variation, patterned photoresist is formed on the semiconductor substrate 10, shape of patterned photoresist 11 could be any shape, and both location and shape of trenches 12 are random distributed.
Obviously, line width variation and non-smooth surface changes the shape of patterned photoresist, increases the critical dimension of patterned photoresist and disagrees the pattern on the semiconductor substrate with the actual shape. Thus, conventional semiconductor fabrication usually repairs patterned photoresist to reduce or eliminate line edge roughness of patterned photoresist before pattern of patterned photoresist is transferred into the semiconductor substrate.
Conventional semiconductor fabrications reduce line edge roughness of patterned photoresist by modifying temperature and/or period of soft bale process, hard bake process, and/or post exposure bake process. However, because standing wave phenomena is unavoidable while patterned photoresist is exposed by light and improvement is limited by the available material of patterned photoresist, conventional semiconductor fabrication could not effectively reduce, or even eliminate, line edge roughness of patterned photoresist.
As the following summary, the conventional semiconductor fabrication could not prevent defects of line edge roughness. Effects of line edge roughness are more and more serious while critical dimension of semiconductor device being continuously shrunk, it is desired to develop a new method for reducing line edge roughness of patterned photoresist.
One main object of this invention is to reduce line edge roughness of patterned photoresist effectively.
Another main object of this invention is to improve precision of patterned photoresist without changing patterned photoresist material or changing both develop process and bake process.
Still one main object of this invention is to reduce line edge roughness by filling, to accomplish good control ability for control line width of patterned photoresist effectively.
This present invention provides a method of reducing line edge roughness of patterned photoresist. Initially, provide a patterned photoresist which has at least a trench and is located on the substrate. Then fill these trenches so let that trenches are totally filled by an additional material, wherein the additional material is easily to bond with the patterned photoresist. Next, remove parts of the additional material that are located on patterned photoresist and the substrate. Finally, treat the additional material to enhance that adhesion between the additional material and patterned photoresist after the additional material is treated. Because trenches on patterned photoresist are filled by the additional material, real pattern of patterned photoresist could be equal to the ideal pattern, and then precession of patterned photoresist is enhanced.
Furthermore, this embodiment could be further modified as follows: omit step of removing part of the additional material while only trenches are filled by the additional material; and omit step of treating the additional material while adhesion between the additional material and patterned photoresist is good.